The present invention relates to a wheelchair having an anti-tip system for preventing overturn of the wheelchair. More particularly, the present invention relates to an anti-tip system for a reclining wheelchair in which the anti-tip members are connected to the pivoting seat.
Wheelchairs, whether manually operated or motor driven, typically include a wheel-supported base and a seat having back and bottom portions supported on the base. Under conditions of sudden accelerations or decelerations, wheelchairs may be subjected to forces tending to overturn the wheelchair. It is known to provide wheelchairs having anti-tip members extending from the wheelchair to prevent overturn of the wheelchair. The anti-tip members are typically not ground engaging but, instead, are supported so as to contact the ground surface upon pivoting of the wheelchair in an overturn situation, thereby preventing complete overturn of the wheelchair. The anti-tip members typically include a wheel which provides for controlled contact between the ground surface while the overturning wheelchair is moving.
The anti-tip members may extend rearwardly from the base to limit rearward overturn that might occur, for example, if the wheelchair is accelerated to ascend an incline surface or to overcome an obstacle such as a curb. It is also known to include forwardly extending anti-tip wheels to prevent forward overturn of the wheelchair that might occur if the wheelchair were to be suddenly decelerated on a decline surface.
A problem associated with many anti-tip systems of the prior art is caused by the rigid connection between the anti-tip members and the wheelchair. Sudden stoppage of a rearwardly overturning wheelchair by contact of an unyielding anti-tip member and the ground surface may transfer jolting forces to an occupant potentially resulting in whiplash-type reactions.
Many invalid or handicapped persons are in their wheelchairs for extended periods of time. Lengthy confinement of a person in one position in a wheelchair, however, can lead to discomfort or even sores, resulting from a lack of circulation. It is, therefore, desirable to provide a reclinable wheelchair in which the seat of the wheelchair is pivotably supported on the base of the wheelchair. The pivoting of an occupant with respect to the base facilitates blood circulation thereby providing relief for the occupant.
Reclining of the wheelchair seat, however, shifts the center of gravity for the occupied wheelchair rearwardly. This shift in the center of gravity increases the tendency of the wheelchair towards rearward overturn (i.e., reduces the wheelchairs rearward pitching stability). A significant shift in the center of gravity may even result in a static load condition in which the force of gravity alone acting on the occupant is sufficient to overturn the wheelchair. Under such conditions it would be desirable for the wheels of the anti-tip member to be ground-engaging wheels (i.e., contacting the ground) such that pivoting of the wheelchair base with respect to the ground surface is completely prevented.
U.S. Pat. No. 5,137,295 to Peek discloses a rear anti-tip system having anti-tip members pivotably connected to the base of the wheelchair. Linkage members are pivotably connected to the anti-tip members and to the back of the seat to convert pivoting of the seat to pivoting of the anti-tip members. The linkage members, however, are rigid members. As discussed above, stoppage of an overturning wheelchair having such an unyielding linkage system will be sudden and jolting with respect to the occupant. Furthermore, the direct connection between the seat and anti-tip members by the linkage member means that the anti-tip members will be required to be pivoting with the seat throughout the entire range of pivot of the seat. Such pivoting of the anti-tip members may require that they have a raised position with respect to the ground surface that is excessively large for the anti-tip members to effectively prevent overturn of the wheelchair due to acceleration (i.e., acceleration overturn). To ensure that the raised anti-tip members in U.S. Pat. No. 5,137,295 can prevent acceleration overturn of the wheelchair it would be necessary to restrict the amount of pivoting of the seat to limit the required pivoting of the anti-tip members.
According to a first embodiment of the present invention, there is provided a stabilizing system for a wheelchair having a seat pivotably supported on a base. The stabilizing system includes at least one anti-tip member pivotably connected to the base at a pivot axis. The system may include a wheel rotatably connected to the anti-tip member adjacent one of its ends. The system further includes an anti-tip actuating cable operably connected to the seat and to the anti-tip member such that pivoting of the seat causes the cable to pivot the anti-tip member.
The wheelchair may include a lift assembly for pivoting the seat with respect to the base. The lift assembly includes at least one arm pivotably connected to a bottom portion of the seat and to the base. The actuating cable is secured to the arm of the lift assembly to provide for translation of the actuating cable as the seat is pivoted by the lift assembly.
According to a second embodiment of the invention, a powered wheelchair includes at least one drive motor engaging one of a pair of drive wheels. An anti-tip member is secured to the drive motor to form a suspension assembly. The suspension assembly is pivotably connected to the base at an axis such that the drive motor is located forwardly of the axis and at least a portion of the anti-tip member extends rearwardly from the axis. An actuating cable is connected at a first end to the suspension assembly forwardly of the axis. The cable is operably connected to a bottom portion of the wheelchair seat. The powered wheelchair preferably includes a recline assembly having at least one lift arm pivotably connected to the seat bottom and to the base with the cable being secured to the lift arm. The seat is preferably translatable with respect to the base for powered translation by a drive member.
According to a third embodiment of the invention, a stabilizing system is provided for a wheelchair. The system includes an anti-tip pivot control mechanism having an axially compressible spring. The control mechanism engages an actuating cable for a pivoting anti-tip member such that translation of the actuating cable results in compression of the spring. The compression of the spring provides a predetermined amount of seat pivot occurring without a corresponding pivot of the anti-tip member. Preferably the control mechanism includes a first member secured to the cable adjacent its first end and a second member secured to the anti-tip member with the spring being located between the first and second members such that translation of the cable results in compression of the spring.
According to a fourth embodiment of the invention, a reclinable wheelchair is provided which includes a pivoting anti-tip member that is upwardly biased by a spring. The wheelchair includes a linkage system connecting the seat to the anti-tip member to transfer pivot of the seat to pivot of the anti-tip member. The linkage system includes first and second members that are pivotably connected to one another. The second linkage member is axially compressible to provide for a predetermined amount of seat pivot without corresponding pivot of the anti-tip member. Preferably the second linkage member includes portions that are slidable with respect to each other and a spring engaging the portions of the second linkage member for biased extension of the member.